Designers of contemporary communications devices face numerous challenges. Such challenges arise from a continued increase in the levels of semiconductor device integration in addition to constantly striving to reduce power consumption, size, and cost, while increasing capabilities. Wired and wireless communication devices are no exception. In traditional broadcast systems where one device is broadcasting to many receivers, it is possible, and often practical, to design the broadcasting system to more rigorous specifications. However, in a distributed network or other like environment, it is not always practical from a commercial standpoint to design each of the devices in accordance with the highest standards. Accordingly, in contemporary communication devices, a low-cost, practical implementation of the physical layer presents a unique challenge in view of variations associated with device componentry.
One such challenge involves the imbalance that typically occurs between the in-phase (I) and quadrature-phase (Q) branches when a received radio frequency (RF) signal is down-converted to baseband. Similarly, at a transmitter, IQ imbalance can be introduced during frequency up-conversion from baseband to RF. IQ imbalance can be the result of “amplitude,” “phase,” and “delay” mismatch between the I and Q branches in quadrature heterodyne communications. Particularly, in typical communication systems, the gain (amplitude) and phase responses of the I and Q branches can be different from one another, resulting in signal distortion. The IQ imbalances can limit the achievable operating signal-to-noise ratio (SNR) at the receiver, which can adversely impact constellation sizes and data rates. This imbalance can occur with both heterodyne receivers as well as with the so-called zero-IF, or direct-conversion receivers. Although a direct conversion receiver is preferable for low-cost and power-sensitive applications, it tends to be more sensitive to IQ imbalance. With IQ imbalances, translated spectral components from both the desired frequency bin and the associated “image” frequency bin come into play, although the former usually dominate.